It is not the first time artificial sweeteners are linked to negative effects on human health, such as weight gain or diabetes. But a new study by Suez et al. now published in Nature might very well mark an important cornerstone in our perception of artificial sweeteners as a frequently used food additive.

At first it seems very counterintuitive that a so called ‘non-caloric’ sweetener can contribute to trigger diabetes or obesity, after all it is non-caloric, or ‘zero calories’, right? Like so often, however, reality again proves to be much more complex than that. It is true that artificial sweeteners cannot be used by our body as a ‘fuel’ such as conventional sugars and hence have no calories. But only looking at calories is far too simple as it turns out.

Practically every piece of us, in particular our guts are covered with a myriad of microorganisms such as bacteria that turn our guts into an incredible complex ecosystem (see also my latest blog post on this little universe called the ‘microbiota’). Those microbes play an essential role in digestion and the gut microbe composition is able to quickly adapt to changing conditions, for example changing diets1.

Gut microbes were cultured under controlled conditions with and without saccharin, and then transferred back into mice. Mice that got cultured gut microbes form the saccharin-rich sample had a much higher level of glucose in their blood (an indicator for glucose intolerance).

Suez et al. now demonstrated that mice feed with artificial sweeteners especially saccharin rapidly develop glucose intolerance (glucose is a very frequent conventional sugar) and also show a heavily altered composition of their gut microbiota2. The authors could even show that the artificial sweetener causes the drastic transformations in the gut ecosystem which is then the reason why the mice develop the glucose intolerance. They did so by culturing gut microbes in the presence or absence of saccharin. When transferred back to normal mice the ones which got microbes grown in the presence of saccharin had a higher chance of developing the glucose intolerance (see my 2nd figure).
In addition, a small number of human testers also changed to a saccharin-rich diet for one week. About half of them indeed showed much higher glucose levels in their blood. So my gut feeling tells me: don’t play with your microbes! Feed them with good stuff, and not with artificial sweeteners…3

Reference

Actually, microbes divide and hence mutate fast. In addition the microbiota is a very diverse mixture of many microbes which all interact in one way or another (for instance because they compete for nutrients). This makes it possible to undergo quite drastic changes in a relatively short amount of time (days). See also my other post on the microbiota. [↩]

Microbiota or sometimes ‘microbiome’ stands for all the microorganisms that live in and on top of us. [↩]

Yes. Of course. Strictly speaking, this study doesn’t prove or disprove that artificial sweeteners are also having a negative effect on human health under real life conditions comprised of a large variety of foods and sugars and usually much longer adaptation time towards sweeteners for the people that consume them regularly. However, it elaborates on one potential scenario that could very well be highly relevant in daily human lives. An most of all, I really like that it shows how complex and non-trival food and medicine related issues most of the time turn out to be. Exchanging sugar against artificial sweeteners hence does certainly NOT only exchange calories against no-calories, but it clearly has some effect on the gut microbiota (whether this change is good, bad, neutral… that has to be evaluated in many more studies focusing more on human diets and behavior). This is by the way a very intrinsic problem in nutritional science. Everything is highly linked and thus extremely complex. And perfect ‘control groups’ hardly exist… I guess in general it’s not too bad to remain fairly skeptical when people make too bold statements saying this and that ingredient is totally evil or totally healthy. Reality is never that simple. [↩]